Infrared (IR) detectors, for example, far IR detectors may be operated with additional optical elements, such as multifocal Fresnel lenses. For example, pyro-electric detectors traditionally consist of two oppositely connected heat sensing elements. The two heat sensing elements cancel out commonly received radiation, such as impinging sunlight, and thus need an optical system illuminating the radiation of a localized moving heat-spot for example, a person, onto only one of both elements.
FIG. 1 is a schematic, cross-sectional side view of a typical detector 100 configured to detect the position, motion and/or direction of a living being (e.g., a human) within a monitored space. In general, the phrase “monitored space” refers to a physical area (e.g., a room, hallway, outdoor area, etc.) where the detector 100 is positioned and where the detector 100 can potentially detect the living being. The field of view (FOV) of the detector describes a region where the detector is capable of sensing a warm object, and may be a portion of the monitored space, or may include all of the monitored space.
The detector 100 has a sensor module 102 with one or more thermal sensing devices (e.g., thermopiles) and a lens array 104 at least partially covering the sensor module 102. The lens array 104 has a plurality of lenses, each of which is arranged to direct incident thermal energy from the monitored space onto at least part of the sensor module 102. Each individual lens may direct incident thermal energy from one of multiple different physical zones in the monitored space onto the sensor module 102.
An integrated circuit 106 that may, in various implementations, form a computer-based processor, a computer-based memory storage device and/or other circuitry to perform and/or support one or more of the functionalities described herein. Electrical conductors (e.g., traces that extend along the upper and/or lower surfaces of the substrate 110, vias 108 that extend through the substrate, solder bumps 112, etc.) are provided to connect the electrical components of the detector 100 to external components.
Thermal sensing devices such as thermopiles or photonic detectors are generally operable to produce a direct current (DC) output that is substantially proportional to an amount of thermal energy being received at that thermal sensing device. The DC output produced by such a thermal sensing device generally remains constant as long as the amount of thermal energy being delivered to that thermal sensing device remains generally constant. Increases in the amount of thermal energy being delivered to the thermal sensing device generally result in a proportional increase in the DC output being produced by that sensing device. Likewise, decreases in the amount of thermal energy being delivered to the thermal sensing device result in a proportional decrease in the DC output being produced by that sensing device. The DC output from the thermal sensing devices may be either a DC voltage or a DC current.
Present motion detectors typically employ pyroelectric materials, often in conjunction with the lens array 104 to detect the movement of people in a room. A pyroelectric material generates a signal if the incoming heat radiation (from a heat source such as a human body) changes. Mathematically, the pyroelectric detector generates an electrical signal that follows the time derivative of the incoming heat flux. Thus, if a person enters or leaves the detector FOV, the heat flux changes and a respective signal is generated. The amplitude of the signal is dependent on the temperature of the heat source and the so-called filling factor of the FOV. The higher the temperature of the source and the more the source fills the FOV of the detector, the higher the resulting signal.
A warm object radiates heat which can be sensed with thermal sensors such as pyroelectric sensors, thermopiles, bolometers, etc. In case the object is moving through the field of view of such sensors, the amount of radiation changes over time. To distinguish the variation in time from the movement of that object (the signal) from a variation in time which originates from local heat sources that change in temperature and thus the amount of radiation (the background), the background may be removed from the signal. This is called background subtraction.
Traditionally pyroelectric detectors implement a combination of a scrambling optic and at least two sensing elements separated in space. The scrambling optics segment portions of the FOV the object is moving through into segments such that the change of net radiation on one of the elements is fast enough to be sensed, and the net radiation seen by the individual elements is significantly different. This approach is depicted by FIG. 2. At least 2 sensing elements 221, 222 are connected together such that commonly received radiation is canceled out at the electrical output 231, 232 and does not give any variation of the resulting signal 230 over time 240. If the ambient for example is heating up or cooling down, the amount of radiation rises or falls but is commonly seen by both elements and thus not sensed. To generate a signal 240 in that sensing element combination, one sensing element 221 must see a different amount of radiation than the other sensing element 222.
To observe movement of the object in the field of view of the sensor, the radiation received on the sensor varies in space as well as time. This is realized by scrambling optics which project the position of the object on one of the elements 221, 222 depending on the position of the object in the FOV. A movement of the object through the FOV results in an unbalanced change of the radiation on the sensing elements which in turn generates a non-zero signal 240. In general the object must change the position from one zone (AB 210) to another (B/A 210) in order to be sensed. Objects remaining in one zone are not sensed.
However, traditional single-element pyro-electric detectors cannot sense a DC component of the received radiation, and thus have used a modulated radiation to provide an output to back end processing electronics. Therefore, there is a need in the industry to overcome one or more of these limitations.